Electronic keying circuit with one negative and one positive voltage output



Feb. 21, 1950 USSELMAN AND ONE POSITIVE VOLTAGE OUTPUT G. ELECTRONICKEYING CIRCUIT WITH ONE NEGATIVE Filed May 16, 1944 3 Sheets-Sheet 1INVENTQR 650%: Z. 055:: All/V.

MV'M/ ATTORNEY Feb-21, 1950 c; USSELMAN V 7,

ELECTRONIC KEY'ING' CIRCUIT WITH oNE NEGATIVE AND oNE POSITIVE VOLTAGEOUTPUT Filed May 16, 1944 3 Sheets-Sheet 2 INVENTOR 550/2 4- 1. (Am-:44144/.

ATTORNEY Feb. 21, 1950 s. L. USSELMAN 2,

7 ELECTRONIC manna QIRCUIT WITH om: NEGATIVE AND ONE POSITIVE VOLTAGEOUTPUT Filed May 16, 1944 3 Sheets-Sheet 3 Our/ ur 0 am; Joana- INVENTOR62-04%! Z. Max-1mm ATTORNEY Patented F eb. 21, 1950 ELECTRONIC KEYINGCIRCUIT WITH ONE NEGATIVE AND ONE POSITIVE VOLTAGE OUTPUT George L.Ussehnan, Port Jefferson, N. Y., assignor to Radio Corporation ofAmerica, a, corporation of Delaware Application May 16, 1944, SeriaI No.535,829

2 Claims.

This application discloses improved means for deriving from potentialsor current the amplitude of which varies between two values, otherpotentials which vary as desired about a selected base value, which maybe negative or positive as desired. The potentials may be derived fromA. C. pulses or from varying direct current potentials.

This means may be considered single ended in that one output potentialso varying is derived or put to use. Two potentials may be derived whichvary differentially about selected base values. The base values may bothbe negative or both positive or one negative and the other positive. Thederiving means may then in a sense be considered double ended and ashaving a differential output since the two potentials vary in adifferential manner.

The means of this application may be put to various uses, as will beapparent to one skilled in the art. In a preferred application thederived potential or potentials are used to control or key a transmitterfor the production of Wave energy of carrier wave frequency, thefrequency of which is shifted between two values, one of which denotes amarking condition and the other of which denotes a spacing condition. Inthis case the original potentials or currents represent signals to be\put on the carrier wave for communication purposes. Systems for thiskind of transmission are known in the art as spaced wave keying orfrequency shift keying systems.

A general object of this invention is then the production of potentialswhich vary as desired about a base value.

Another object of this invention is the production of potentials whichvary as desired about a base value which may be positive or negative andthe variation may be from a positive value to a less positive value orfrom a negative value to a less negative value or from a positive valueto a negative value and vice versa.

Another object of this invention is the production of potentials ofsubstantially square wave form, which potentials .vary about a basevalue of approximately zero, the potentials being alternately positiveand negative in value.

An additional object of this invention isthe production of twopotentials as described in the preceding paragraphs which varydifferentially.

A further object of this invention is to convert varying direct currentpotentials or pulses of A. C. into unidirectional currents of squarewave form to insure certain and reliable square wave balanced keying ofthe frequency of wave energy when the produced unidirectional currentprovides potentials for keying a frequency shift transmitter.

A further object of this invention is to convert varying direct currentpotentials or pulses of A. G. into energies of square wave form and oflimited amplitude. In other words, an object of this invention is energyconverting in such va, way as to provide current limiting. That is, aninput signal of varying amplitude produces an output signal having anadjustable constant or uniform amplitude.

A still further object of the present invention is the production ofpotentials as described above under the control of signals such as usedin telegraphy systems.

Th manner in which the above and other objects are attained and thebenefits derived from attaining the same will now be described indetail. In this description reference will be made to the attacheddrawings wherein Figs. lto 3, inclusive, each illustrate by wiringdiagram the essential features of my improved means for deriving controlor keying potentials. In each of these embodiments the means forderiving the potentials is shown as being controlled by keyed currentsor pulses of alternating currents, both representing signals and theproduced potentials are described as being used to key (frequencymodulate) transmitter circuits. It will be understood that the produced.pulses may be put to other uses.

As stated above in describing my improved system, it will be assumedthat the same will be excited by keyed currents (D. C. or A. C.) and itsoutput is to key or modulate the frequency of a wave generator forfrequency shift telegraphy. The system is of broader application.

In Fig. 1, the keying-tripping circuit is similar I to thatshovvn inFig. 3 of my U. S. Patent #2326314, dated August 10, 1943. The tubes V3and VA are arranged in a tripping circuit of the type shown in FinchPatent #1,844,950. As

arranged, these tubes have their control grids cross-coupled to theiranodes by resistances 34 and 36 in sucha manner that when the grids areso excited that one of the tubes, say for example, V3, draws current,the potential drop in resistance 35) grows and resistance 34 appliesamore negative potential to the grid of V4, so that this tube draws lesscurrent and the potential drop in the resistance 32 decreases andresistance 36 applies a more :positive potential to the grid of tube V3to expedite the switching of current of the system through tube V3. Thepotential at the anodes of tubes V3 and V4 when operated as describedabove, alternate differentially by tripping suddenly between positiveand less positive values which may be varied to suit the needs at handby changing the resistance values and the amount of D. C. potentialapplied to the adjacent ends of resistances 30 and 32. Excitationapplied in such amanner as to'start current through V4 reverses theoperation to switch the current through V4.

In the present application, thecontrol grid [8 and cathode of V3 areconnected together by resistance 38 and potentiometer resistance 46 andbias resistor R5 shunted by a condenser 64 which is sufiicientlylarge-to form a path of low impedance to potentials of the keyingfrequency. The control grid l2 of tube V4 is similarly connected to thecathode of tube V4 .by resistance 40, resistance 48 and resistance R5.Varying impulses (keyed D. C. or A. C.) are applied to-the potentiometer48 at contacts 49 and 51.

The arrangement is such that in the absence of signals the bias on thecontrol grid it of V3 is negative and switches the current through thetube V4, as described above. Bias is obtained by the cathode resistorR5. The grids are at difierent potentials due to the potentiometeraction of resistors 36, 38, 46 and resistors 34, 4D, 48. The requirednegative bias may be produced by the potential drop in resistances 45and 38 due to currents from resistor 36 and the cathode current in R5.If this bias is insufiicient, itmay be supplemented by negativepotential from source so by closing switch 52 on the left hand contact.However, usually sufiicient bias is obtained during operation withoutthe use of source 50. It can be seen thatgrids l and I?! are atdifferent positive :potentials. At no signal, grid i0 is less positivebecause R46 is partially shorted or has a negative potential applied toit. The application of a stronger negative potential by the signal toR48 .causes grid [2 to be less positive than grid l0 which trips thecurrent in the tubes. If during keying the bias produced in resistances38 and 46 and R is-so highly negative that the negative markingpotentials are unable to switch the current from tube V4 to V3, theswitch 52 is closed in the right hand position to short out a variableportion of resistance 46. When theadjustment is as described above, andvarying potentials are to; be applied to control the tripping circuit,and the output is used to key a transmitter, the current is switchedthrough tube V4 to make the po- ,tential at the anode of tube V4 lesspositive and the-potential at the anode of tube V3 more positive, thesystem may be considered as in the spacing condition, which is also thecondition at which no signal markings are being sent out.

Now, if a negative potential, representing marking potential, is appliedto the potentiometer 48 and thence to the grid 12, this negativepotential overcomes the spacing bias efiect to switch current from V4 toV3.

When this negative marking potential is removed or is insuflicient thecircuit trips current back through the tube V4 which, as stated above,is the spacing condition. The application'of A. C. pulses at 49 in likemanner operates the tripping circuit because the negative alternationsthereof make the grid I2 more negative and current is tripped throughtube V3.

Moreover, A. C. keying causes the tripping circuit to function withoutthe aid of bias 50 and 52.

However, a bias is needed in case the signal is re- .moved so as to holdthe transmitter on space. -While this action is taking place thepotentials on the anodes of the tubes V3and V4 are switched morepositive and less positive differentially and vice versa, so that acrossthese anodes and across resistances 30 and 32 therebetween we havepositive potentials which vary differentially as the system is keyed andthese positive potentials are of square wave form of constant amplitude.The tripping not only squares up the keyed wave but limits its amplitudeand produces across the resistances 3B and 32 potentials of wave formideal for keying purposes.

The outer ends of the resistances 30 and 32 are connected as shown tothe anodes of tubes V3 and V4 in the tripping circuit. Adjacent ends ofthe resistances 30 and 32 are connected to a positive supply source andare grounded for potentials of the keying frequency by condenser 3|. Thedifferentially varying potentials described above appear at the anodeends of resistances 30 and 32 and may be used therefrom directly ifdesired. In the present embodiment, I desire to provide at the points Aand B positive potentials which vary difierentially above selectedpositive base values but remain positive irrespective of the saidvariations. To do this two potentiometer resistances 52 and 54 havetheir outer ends connected to the anode ends of'resistances 30 and 32,and their adjacent ends grounded for potentials of the keying frequencyby condenser 56 and also connected to a point on the potentiometerresistance 6!] for positive supply bias at the points A and B.

It can be seen that by moving the points on 52, 54, various degrees ofcoupling and various amounts of signal wave may be obtained at thepoints A and B. At A and B it is assumed that positive potential is tobe used say, for example, to "apply to the screen grids 22 and 24 of afrequency modulated oscillation generator such as described -in my abovementioned-patent, and that direct current will also be supplied to thesegrids.

The positive potential is supplied from 60 to the adjacent ends ofresistances 52 and 54 to lighten the direct current load on the trippingcircuit and to maintain this positive bias on the screen grids 22 and 24as the leads 59 and 6| are moved towards the adjacent ends of thepotentiometers or to the lower coupling position.

Potentiometer 50 is additional means for adjusting the bias at A and B.For example, if variable signal coupling is obtained by tapping leads 59and ti on resistors 52 and'54, the positions of low coupling are thepoints of highest screen grid bias potential for tubes VI and V2,

which is not a desirable adjustment. Again for instance, if the loweradjacent ends of 52 and 54 were grounded directly for D. C. (say bymoving the tap on potentiometer 60 to the right end thereof) or leftungrounded (i. e., the lead to potentiometer broken), the positions oflow signalling coupling would be the points of lowest bias at points Aand B, which is also undesirable. In other words, the adjustment ofpotentiometer 60 fixes a lower limit on the positive bias potential at Aand B (for the screen grids of tubes VI and V2) as the coupling islowered. Adjusting the coupling between the tripping circuit and thefrequency modulation oscillators V! and V2 results in adjusting theamount of transmitter signal frequency deviation.

The condenser 64in shunt to R5 has the effect of slightly rounding offthe corner on one end of each square wave signal character. A moresatisfactory way of rounding off the corners of thesquare wave signalcharacters is to connect 59 and GI. A single section low pass filter isshown in each of the leads 59 and 6| in Fig. 1.

Several sections may be cascaded if desired. These filters arepreferably dimensioned to cut ofi at frequencies three or four times thekeying frequency, or enough to round off the corners of the producedsquare wave keying potentials. The reason for rounding off the cornersof the signal characters is to limit or reduce the frequency band widthcaused by harmonics.

In the arrangement of Fig. 1, it will be noted that the potentials at Aand B are positive and vary differentially about positive valuesselected by adjustment of potentiometer resistances 52,

.54 and 30. In some cases, it is desired to provide potentials at A andB which vary positive and negative about a selected value which may bepositive or negative or zero potential. Then an arrangement asillustrated in Fig. 2 is used. This arrangement is substantially asillustrated in Fig. 4 of my U. S. Appln. Serial #521,907, filed February11, 1944, now Patent Number 2,461,456, issued on February 8, 1949.

In this embodiment the potentiometer resistance 60 is in shunt to asource B3 of D. C. potential the positive terminal of which is groundedso that a variable negative potential is applied to the adjacentterminals of resistances 52 and 54. When the tripping circuit includingthe tubes .V3 and V4 is keyed as described hereinbefore,

the potentials at the anode ends of resistances 30 and 32 arealternatively more positive and less positive and vary differentially asdescribed hereinbefore. The outer ends of the resistances 52 and 54 thenare differentially excited by these alternately varying positivevoltages, the alternations taking place in accordance with the keying ofthe input of the tubes V3 and V4.

As in Fig. 1, the source 5|] is sometimes necessary to apply negativebias to the grid of tube V3 in order to get a positive or sure trippingaction. The setup is such that the tube V3 is biased to cutoff in theabsence of marking and spacing signals either by the drop in resistances38 and 45, or if necessary, by the negative potential from source 55.The current is then switched through tube V4 so that the positivepotential at the anode of tube V4 falls. The resistances 52 and 54 andthe tap on 69 etc., are so adjusted that the desired negative potentialis supplied, by source B3 and the potential at the anode of V4, to line6| and at point B. The value of the negative potential developed at B isadjustable by adjusting the taps on 52, 54, and 69. This of courseadjusts the coupling of the tubes V3 and V4 to the output at A and B.Where the potential is used to block a tube such as, for example, tubeV2, the potential at B is made sufliciently negative to block this tubefor reasons described in my last mentioned application.

At the same instant, the potential at A is posi tive because the currenthas been switched through tube V4. Tube V3 is cut ofi and little or nocurrent flows therethrough. The potential at the anode of V3 has becomemore positive and is with Fig. 1, in the absence of signals at contacts5| and 49, current, is switched through the tube v4, while tube v3, is.blocked. -:The current:

through the tube V4 produces an increased drop in potentialthrough'resistance 36 so that at B a negative potential is developed toblock the tube V2. At the same time a positive potential is developed atthe point A. Now when signals are applied to connections 5| and 49 andare sufliciently negative, the current is switched from tube V4 to tubeV3 and the operation is as described above, so that tube V4 is blockedand the potential on the grid of tube V3 becomes more positive to switchthe current through tube V3. This applies a negative potential at thepoint A and to the screen grid of tube VI to block this tube. At thesame time a positive potential is applied from the anode of tube V4 tothe end of resistance 54, and through the tap thereon to the point B andthe screen grid of tube V2 so that this tube becomes conductive.

The keying potentials at 5| and 49 may be alternating current or directcurrent pulses. Alternating potentials may be applied to the input 49.When alternating current and voltage is applied across terminals 5| and49 it is usually done through a transformer, the primary winding ofwhich is excited by the A. C. and the secondary winding of which isconnected to points 5| and 49. During one part of the control potentialcycle the grid of tube V4 is biased positive and during the other partof the cycle the grid of tube V4 is biased negative. This is evidentwhen it is remembered that alternating currents are caused by alternatesurges of positive and negative potential. The resistances 34 and 36 areof a higher value than the resistances 38 and 40 so that the positivebias from th tube anodes is overcome when negative bias is applied.During operation when switch 52 is closed the grid of tube V3 is morenegative than the grid of tube V4, when no signal or when positive sig-4 nal is applied to the grid of tube V4. When a is suddenly out 01f andtube V3 carries large current. When terminal 49 goes to zero or positivepotential the circuit suddenly trips back to the original condition oflarge current in tube V4 and no current in tube V3. Switch '52 is closed50 on contacts or 2 when only negative pulses or potential are appliedto terminal 49. If alternating positive and negative potential pulsesare applied to terminal 49 when switch 52 is left open and satisfactoryoperation obtained.

56 The potentials at A and B may be used to key tubes VI and V2 on andoif by controlling the same by acting on the screen grids. If thepotentiometer points on resistances 52 and 54 are correctly adjustedalternately positive and nega- 00 tive pulses of the proper valuesappear at A and B. Adjustment of 52, 54 and 69 makes the control oftubes VI and V2 as sure as desired. The potentials are of constantmaximum amplitude because of the limiting action of tubes V3 and V4, andare also of square wave form.

In other cases, it is desired to produce at points A and B potentialswhich vary about selected values, one negative, the other positive. Anarrangement as illustrated in Fig, 3 may then 70 be used.

In this arrangement the keying-tripping circuit including tubes V3 andV4 is connected and arranged as described hereinbefor in connection withFigs. 1 and 2, except for the following changes. The ends ofpotentiometers 52 and 54,

'7 'insteadof being connected together and to a tap on potentiometerresistance 60 as in the prior modification, are now connected to pointson potentiometer resistances 60' and 60". The potentiometer 69 shunts asource the positive end of which is grounded so that the tap onpotentiometer 52 supplies a negative potential of adjustable value tothe point A. The potentiometer resistance 69 has its negative terminalgrounded so that the tap on the potentiometer 54 supplies a positivepotential of adjustable value to the point 'B. As the tubes V3 and V4are tripped so that the current is suddenly switched from one to theother thereof and vice versa under control of the potentials from thesignal source, the positive potentials at the anode ends of resistancesand 32 swing up and down differentially, as described hereinbefore. Thevariable positive potential at the anode end of resistance 36 incombination with the desired negative potential supplied topotentiometer resistance 52 produces at the point A a negative potentialof adjustable value which varies up and down as the tubes V3 and V4 arecontrolled.

The variable positive potential at the anode end of resistance 32 withthe positive potential supplied to 54 produces at the point B a varyingpositive potential the variations of which follow the control of thetubes V3 and V4. Both of these steady or direct currcnt'potentials areadjustable by means of potentiometers 60 andfifl". The base value of oneis negative and the base value of the other is positive.

In operation, if the tube V3 carries current and the tube V4 is cutoffthe negative bias at the point A goes more negative and the positivebias at the point Bgoes more positive. If tube'V i carries current andtube V3 is cutoff, then the negative potential at the point A becomesless negative and the positive potential at the point B becomes less,

positive. By appropriate adjustment of the potentiometers 52, 54, 60',and 60", alternating positive and negative biases may be obtained atpoints A and B. If it is generally desirable with this arrangement tohave only varying negative, biases in this circuit, such may be obtainedby sliding the potentiometer pointfill toward the lower potential end ornegative end of the source shunted by the potentiometer.

The varying negative and positive potentials,

at A and B may be put to any use. In my U. S. application Serial#535,828, filed Ma 16, 1944, now Patent Number 2,454,954, issuedNovember 30, 1948,- the potential at B is shown as being used screengrid of an oscillation generator tube VI to shift the'frequency of theoscillations generated in accordance with signals from the signal sourceconnected to points 49 and 5|. The differentially varying potential atthe point A is shown as' being used to supply a differential actingcompensating potential to the control grid of the oscillation generatorto compensate and reduce undesired amplitude modulation resulting fromthe frequency shift process.

In Fig. l of U. S.-Patent #2,326,-3l4, and in Fig. 4 of my U. S.application Serial #521,901, filed February 11, 1944, the screen gridsof tubes VI and V2 are connected to the cathodes by condensers whichby-pass the radio frequency currents on the screen grids so that thesaid screen grids operate at substantially zero radio frequencypotential and consequently act as shields or screening electrodes. Thescreen grid I2 of Fig. 5 of my U. S. application Serial #535,828,

to control the direct current potential on the;:

8 filed May 16, 1944, now Patent Number 2,454,954, issued November 30,1948, operates in a similar manner. In this figure there is also a radiofrequency by-pass condenser connected with the low potential end ofresistance R. and the cathode.

In Figs. 1 and 2 of the drawings in the present application, there isshown a radio frequency bypass condenser between the screeningelectrodes and cathodes of tubes VI and V2. When the leads 59 and 6|include low pass pi-section filters, these by-passing condensers aretaken into consideration in dimensioning the last condenser in thefilters.

If the radio frequency by-pass condensers connected between thescreening electrodes and cathodes of tubes VI and V2 are made smallenough so that they do not materially affect the operation of thefilters, then they can be left in the circuit. If the final condensersin the pisection filters are properly dimensioned they may also serve inthe filter and as radio by-pass condensers between the screeningelectrodes and the cathodes. Then the condensers shown adjacent to tubesVI and V2, between the screening electrodes and cathodes, may beomitted.

The remarks made above apply in full to the end condenser of the lowpass filter in lead 5! of Fig. 3, and substantially in like manner tothe end. condenser in the low pass filter in the lead 59 of Fig. 3. Itis noted that the end condenser in the filter in lead '59 is in shunt toa by-pass condenser between a resistance and the cathode of tube VI.Here again the by-pass condenser may be omitted or taken into account indimensioning the filter condenser.

I claim:

1. In a system of the nature described, a source of electrical energythe strength of which varies, a pair of electron discharge systems eachincluding an electron source, an electron receiving electrode and anelectron flow control electrode, an impedance connected between theelectron receiving electrodes, connections for applying a potentialthrough a tap on said impedance to the electron receiving electrodes,two other impedanccs each having one terminal connected to one of theelectron receiving electrodes, connections to the remaining terminals ofsaid two other impedances for applying to one thereof a negativepotential and to the other thereof a positive potential, an output leadcoupled to each of said other impedances to supply two potentials whichare each a combination of said first named potential and one of saidsecond named potentials, and impedances cross-connecting the electronflow control and electron receiving electrodes, the arrangement beingsuch that when current flows through one of said discharge systems theother is cut off and vice versa to alternately and differentially varythe said first mentioned potential on the electron receiving electrodesto correspondingly vary the supplied potentials when control potentialsare applied to at least one of said discharge systems.

2. In a system of the nature described, a source of electrical energy ofvarying potential, a pair of electron discharge systems each having anelectron receiving electrode and an electron flow control electrode, animpedance connected between the electron receiving electrodes,connections for applying a positive potential through a tap on saidimpedance to the electron receiving electrodes, impedancescross-connecting the electron flow control and electron receivingelectrodes, connections for applying a steady bias to one of saidelectron flow control electrodes, other connections for applying saidvarying potential to said other electron flow control electrode, asource of potential having its positive terminal grounded and itsnegative terminal connected to one of said electron receiving electrodesby a potentiometer resistance, a source of potential having its negativeterminal grounded and its positive terminaI connected to the otherelectron receiving electrode by a potentiometer resistance, andconnections to said last named resistances for deriving therefrom anegative potential and a positive potential which vary difierentially onthe application of said varying potential to said other electron flowcontrol electrode.

GEORGE L. USSELMAN.

10 REFERENCES CITED The following references are of record in the fileof this patent:

UNITED STATES PATENTS Number

